Comprehensive Study Guide for Gestational Trophoblastic Disease (GTD)

Definition and Spectrum of Gestational Trophoblastic Disease

Definition: Gestational trophoblastic disease (GTD) is a group of tumors characterized by abnormal trophoblastic proliferation. The spectrum includes both benign and malignant entities.
Spectrum of Gestational Trophoblastic Neoplasia (GTN):
- Complete hydatidiform mole.
- Partial hydatidiform mole.
- Coexistent mole and live fetus.
- Invasive mole.
- Choriocarcinoma.
- Placental-site trophoblastic tumor (PSTT).
- Epithelioid trophoblastic tumor (ETT).

Histological Classification and Pathology

Division by Presence of Villi:
- Hydatidiform Moles: Specifically contain placental villi.
- Trophoblastic Neoplasms: Lack placental villi.
Gestational Trophoblastic Neoplasia (GTN): Refers to the nonmolar or malignant forms of GTD. This category includes:
- Invasive mole.
- Choriocarcinoma.
- Epithelioid trophoblastic tumor (ETT).
- Placental-site trophoblastic tumor (PSTT).
Occurrence: GTN can emerge weeks or years following any type of pregnancy, though it is most frequent after a molar pregnancy. It possesses the potential to metastasize and can be fatal if left untreated.

Epidemiology and Risk Factors

Demographics: Hydatidiform moles are most prevalent in women aging $< 17$ or $> 35$ years.
History: Previous history of gestational trophoblastic disease increases risk.
Incidence in the United States:
- Occurs in $1$ of $1000$ to $1200$ pregnancies.
- Occurs in $1$ of $600$ induced abortions.
Timing of Diagnosis: Most cases are diagnosed during the first half of pregnancy.
Malar Recurrence Statistics:
- Incidence of a second mole in subsequent pregnancies for patients with a prior partial or complete mole is $1\%$ to $2\%$ .
- Consecutive molar pregnancies necessitate germline genetic testing for mutations in $NLRP7$ and $KHDC3L$ .

Characteristics of Hydatidiform Moles

Hydatidiform Moles (General): Benign placental tumors with malignant potential consisting of villous trophoblast proliferations. Over $80\%$ are benign.
Partial Mole:
- May contain both normal and abnormal placental tissue.
- A fetus may develop but is typically non-viable; miscarriage usually occurs early.
- Genetics: Primarily triploid, resulting from fertilization of an ovum by two sperm or one diploid sperm.
- Malignant Transformation: Local invasion occurs in up to $3\%$ to $5\%$ of cases; metastatic disease is rare ( $< 3\%$ ).
Complete Mole:
- Placental tissue is abnormal and no fetal tissue forms.
- Genetics: Diploid. Most are $46,XX$ (fertilization by a single sperm that duplicates in an enucleated or inactivated ovum). Some are $46,XY$ resulting from dispermic fertilization.
- Malignant Transformation:
  - Approximately $15\%$ to $20\%$ of patients require treatment for GTN after a complete mole.
  - Invasive mole occurs in $15\%$ of cases.
  - Metastatic disease occurs in $5\%$ of cases.
Choriocarcinoma Development: Occurs after $2\%$ to $3\%$ of all hydatidiform moles, with a higher frequency following complete moles rather than partial moles.

Symptoms and Clinical Manifestations

Early Pregnancy Simulation: Initial signs suggest a normal pregnancy, but the uterus often grows larger than expected between weeks $10$ to $16$ of gestation.
Common Symptoms:
- Positive pregnancy test.
- Vaginal bleeding.
- Severe nausea and vomiting (hyperemesis gravidarum).
- Vaginal passage of "grapelike" tissue (strongly suggestive of diagnosis).
Absent Clinical Signs: Absence of fetal movement and fetal heart sounds.
Specific Tumor Symptoms:
- Placental Site Trophoblastic Tumors: Tend to cause bleeding.
- Choriocarcinoma: Often manifests with symptoms related to lung, liver, or brain metastases.
Associated Conditions:
- Hyperthyroidism: More common in GTD; symptoms include tachycardia, warm skin, sweating, heat intolerance, and mild tremors.
- Theca Lutein Cysts: Sometimes present, especially those $> 6\,cm$ .
Subsequent Fertility: GTD does not impair future fertility or increase the risk of prenatal/perinatal complications (congenital malformations, spontaneous abortions) in subsequent pregnancies.

Diagnosis and Evaluation

Diagnostic Tools:
- Serum beta subunit of human chorionic gonadotropin ( $\beta-hCG$ ).
- Pelvic ultrasonography (findings may show a mass containing multiple cysts and absence of a fetus/amniotic fluid).
- Pathology evaluation of evacuated uterine contents or endometrial biopsy.
Clinical Suspicion Criteria:
- Unexpectedly high levels of $\beta-hCG$ (excepting PSTT and ETT, which can produce low levels).
- Uterine size much larger than gestational dates.
- Preeclampsia symptoms in the $1^{st}$ or $2^{nd}$ trimester.
- Unexplained metastases in women of childbearing age with an unknown primary tumor.
Monitoring and Metastatic Work-up:
- Thyroid function tests if $\beta-hCG > 100,000\,mIU/mL$ .
- Imaging: CT of the chest, abdomen, and pelvic area is standard when GTN is diagnosed to check for metastases.
- Pelvic MRI: Used for better visualization of uterine tumors or ovarian theca lutein cysts.
- Metastatic Pattern: Metastases to other sites usually occur only after lung metastases are established.

FIGO Staging for GTN

Stage	Description
I	Confined to the uterine corpus
II	Extending outside the uterus but limited to genital structures (adnexa, vagina, broad ligament)
III	Extending to the lungs, with or without genital tract involvement
IV	Spread to all other distant sites (e.g., brain, liver, kidneys, gastrointestinal tract)

Treatment and Management

Surgical Intervention:
- Suction curettage: Primary method for evacuating hydatidiform moles, invasive moles, PSTT, and ETT.
- Hysterectomy: An alternative if childbearing is no longer planned; it can shorten the duration/amount of chemotherapy needed for remission in low-risk disease.
Chemotherapy (GTN Primary Treatment):
- Low-Risk Metastatic Disease: Often cured with a single agent, such as Methotrexate or Actinomycin D (dactinomycin).
- NCCN Guidelines: Recommend multiday Methotrexate or Methotrexate/Folate regimens. Actinomycin D is used if Methotrexate is contraindicated.
- High-Risk Disease: Requires multidrug combination chemotherapy, possibly with surgery or radiotherapy (RT).
Follow-up and Monitoring:
- Treatment success is defined by at least $3$ consecutive normal weekly serum $\beta-hCG$ measurements.
- Post-Remission Monitoring: Measure $\beta-hCG$ every $2$ weeks for the first $3$ months, then monthly for at least $12$ months.
- High-risk patients require further monitoring at $6$ to $12$ month intervals after the first year of remission.
Contraceptive Requirements:
- Pregnancy must be prevented for at least $6$ months (post-mole) to $12$ months (post-GTN remission) because elevated $\beta-hCG$ from pregnancy interferes with monitoring treatment success.
- Oral contraceptives are typically recommended.

Prognosis and Risk Stratification

WHO Prognostic Scoring System: Used for metastatic GTN to predict mortality risk.
- Low Risk: WHO score $\le 6$ .
- High Risk: WHO score $> 6$ .
Factors Increasing Postmolar GTN Risk:
- Age $> 40$ years.
- Pre-evacuation $\beta-hCG > 100,000\,mIU/mL$ .
- Excessive uterine enlargement.
- Theca lutein cysts $> 6\,cm$ .
Overall GTN Incidence: Approximately $1$ per $40,000$ pregnancies.

Management Flowchart Summary

Mole Identification: Evacuation $+$ weekly $\beta-hCG$ titers.
Careful Follow-up: Includes contraception.
Chemotherapy Triggers: Plateauing $\beta-hCG$ titers or diagnosis of Choriocarcinoma.
Stage-Based Action:
- Stage I: Single drug chemotherapy or hysterectomy.
- Stage II & III: Single drug (low risk) or combination chemotherapy (high risk).
- Stage IV: Combination chemotherapy, surgery, and/or RT.
Resistant Disease: Shift treatment modality if $\beta-hCG$ does not decrease by $\ge 10\%$ over three cycles or increases by $> 10\%$ over two cycles.

Definition and Spectrum of Gestational Trophoblastic Disease

Definition: Gestational trophoblastic disease (GTD) is a group of tumors characterized by abnormal trophoblastic proliferation. The spectrum includes both benign and malignant entities.
Spectrum of Gestational Trophoblastic Neoplasia (GTN):
- Complete hydatidiform mole.
- Partial hydatidiform mole.
- Coexistent mole and live fetus.
- Invasive mole.
- Choriocarcinoma.
- Placental-site trophoblastic tumor (PSTT).
- Epithelioid trophoblastic tumor (ETT).

Histological Classification and Pathology

Division by Presence of Villi:
- Hydatidiform Moles: Specifically contain placental villi.
- Trophoblastic Neoplasms: Lack placental villi.
- Gestational Trophoblastic Neoplasia (GTN): Refers to the nonmolar or malignant forms of GTD. This category includes:
- Invasive mole.
- Choriocarcinoma.
- Epithelioid trophoblastic tumor (ETT).
- Placental-site trophoblastic tumor (PSTT).
Occurrence: GTN can emerge weeks or years following any type of pregnancy, though it is most frequent after a molar pregnancy. It possesses the potential to metastasize and can be fatal if left untreated.

Epidemiology and Risk Factors

Demographics: Hydatidiform moles are most prevalent in women aging < 20 and > 35.
History: Previous history of gestational trophoblastic disease increases risk.
Incidence in the United States:
- Occurs in 1 of 1000 to 1200 pregnancies.
- Occurs in 1 of 600 induced abortions.
Timing of Diagnosis: Most cases are diagnosed during the first half of pregnancy.
Molar Recurrence Statistics:
- Incidence of a second mole in subsequent pregnancies for patients with a prior partial or complete mole is 1% to 2%.
- Consecutive molar pregnancies necessitate germline genetic testing for mutations in $NLRP7$ and $KHDC3L$ .